You may have been puzzled by that curvy weight-lifting bar at your gym: Why all the zig-zags? The advantage of the curling bar, which is also known as the EZ bar, is that it takes pressure off your wrists as you lift, according to exercise scientists at Rensselaer Polytechnic Institute in Troy, New York. Arm curls are the move in which you hold a bar in your hands with your arms hanging down in front of your thighs. You then curl the weight up toward your shoulders. The move primarily targets your biceps, which are the big muscles in your upper arm. But depending on how you hold the bar or dumbbells, you can work other muscles as well.

Standing Bar Curls

You can work the inside and the outside of your biceps with standing bar curls, according to the scientists at Rensselaer Polytechnic Institute. Stand while holding a straight bar or an EZ bar with your arms straight, your palms facing up. The bar should be pressing against your thighs, and your hands will be about shoulder-width distance apart. Slowly bring the weight up toward your shoulders while taking care to keep your back straight and your elbows at your sides. Return to the start position and do several repetitions.

Preacher Curls

Preacher curls target your biceps and your wrist muscles. For the move, you’ll need a preacher bench. Most gyms have one: It has a seat in front of a chest-high pad that slants away from the lifter at a 45-degree angle. While grasping the curling bar in both hands, sit down on the bench and rest your upper arms on the slanted pad. Now lift the weights toward your head, and then lower.

Reverse-Grip Curls

Reverse-grip curls are just what they sound like: curls done while holding the bar in an overhand grip. This move primarily works your upper forearms. Grasp the bar with your palms facing away from you and your hands placed about shoulder-width distance apart. Hold the bar at your thighs. Now, keep your back straight as you curl the bar toward your chest.

Hammer Curls

Work the biceps and the muscles in your forearm with hammer curls. Hold a dumbbell in each hand so that your palms are facing your thighs — imagine you’re holding two hammer handles. Now, lift your right forearm toward your shoulder while continuing to hold the dumbbell in the same way; at the top of the lift, the end of the dumbbell will be pointing at your shoulder. As you lower the right hand, begin to raise your left; continue to alternate arms until you finish your repetitions. Keep your back upright and still throughout.

Concentration Curls

If you don’t have a preacher bench, but want to do curls that really focus on your biceps, you’ll appreciate this move. Hold a dumbbell in your right hand and sit on a bench with your legs spread apart. Lean forward and place your right elbow against the inside of your right knee. Now raise and lower the dumbbell. You’ll find that this position forces your biceps to do all the work by minimizing extraneous body movement that could otherwise assist the lift.

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About the Author

John Hastings has written and edited health, fitness and science stories for magazines, websites and iPad publications. He has held senior editorial positions at "O, The Oprah Magazine," "Reader’s Digest" and "Health." He has also contributed to magazines such as "Men’s Journal" and "Bon Appetit."